1. Field of the invention
This invention relates to an engine part, and more particularly to a highly durable ceramic engine part with excellent heat insulation, heat resistance, and mechanical strength. The "engine part" here refers to a constituent member of an engine, such as a cylinder, a cylinder head, a piston, a precombustion chamber, a port liner, and the like.
2. Description of the Prior Art
These years, from the standpoint of energy saving(s), considerable research and development efforts have been made to improve the thermal efficiency of reciprocating piston engines, such as Diesel engines and spark ignition engines, by using a high engine operating temperature. To operate an engine at a high temperature the engine parts must be made of a heat insulating material with excellent heat resistance. With heat-resistance metals, which have been utilized in making engine parts in general, it has been very difficult to raise the engine operating temperature in excess of the conventional practice due to the limitation of the heat resistance of the metallic material. Recently, a number of studies have been reported which propose engine parts having insulating layers formed of ceramic members with excellent heat insulation, heat resistance, and mechanical strength.
However, the thus proposed engine parts with insulating layers made of conventional ceramic material have a serious shortcoming in that the ceramic members of the engine parts are susceptible to breakage due to generation of a large thermal stress in low-temperature portion thereof in excess of the mechanical strength thereof, because a large temperature difference is generated between the hot portion of the ceramic member exposed to the combustion chamber and the outer low-temperature portion thereof. The large temperature difference is caused by the small amount of heat transfer through the engine parts due to the high heat insulation of the ceramic member and the unitary structure of the heat insulating ceramic member itself.